[GPO]Add a policy for controlling CmdPal enabled state

[jaimecbernardo]

Summary of the Pull Request

Some of the changes for GPO were already on the repo, so this PR just completes functionality.

• Completes the required .admx and .adml files for adding a policy for controlling the enabled state of CmdPal within PowerToys.
• Ports some of the GPO C++ code from the PowerToys source to C# inside CmdPal's codebase, to reduce dependencies on PowerToys.
• Check GPO during CmdPal startup in order to stop execution as soon as possible in CmdPal's lifecycle.

Note: Dashboard in Settings seems to be broken, but that doesn't seem to be caused by this specific PR.

Validation Steps Performed

• Copy "src\gpo\assets\PowerToys.admx" to "C:\Windows\PolicyDefinitions".
• Copy "src\gpo\assets\en-US\PowerToys.adml" to "C:\Windows\PolicyDefinitions\en-US".
• Open gpedit.msc and verify the policy exists in both Computer Configurations and User Configuration.
  
• Exit PowerToys and set the policy to Disabled:
  
• Start PowerToys and verify that CmdPal is disabled in Settings and that you can't enable it:
  
  
• Try to start CmdPal directly and verify it just exits without starting.
• Exit PowerToys and set the policy to Enabled.
• Start PowerToys and verify that CmdPal is enabled in Settings and that you can't disable it:
  
• Remember to set the policies to "Not configured" after validating.